Reducing CSOs in the Big Apple – NYC’s Green and Gray Approach
- Peter J Young, Keith Beckmann, James Mueller, Don Walker
On March 8, 2012, the New York State Department of Environmental Conservation (DEC) and the New York City Department of Environmental Protection (DEP) signed a groundbreaking agreement to reduce combined sewer overflows (CSOs) using a hybrid green and gray infrastructure approach. As part of this agreement, DEP will develop 10 waterbody-specific LTCPs and a citywide LTCP to reduce CSOs and improve water quality in NYC’s waterbodies and waterways. The goal of each LTCP is to identify appropriate CSO controls necessary to achieve waterbody-specific water quality standards, consistent with the Federal CSO Policy and the water quality goals of the Clean Water Act (CWA). This paper will provide an overview of the City’s current and future efforts to cost-effectively reduce CSO in NYC and the challenges of implementing this program.
Receiving water quality in the New York City Harbor has significantly improved over the past thirty years as depicted in Figure 1. Harbor waters are the cleanest in 100 years due to the investment by DEP in new and upgraded wastewater and CSO facilities efforts, however, even with these significant expenditures on water quality improvement, some dead-ended tributary waterbodies still do not meet the primary contact pathogen water quality standard of a monthly geometric mean of < 200 fecal coliform counts /100 ml.
DEP construction projects to reduce and abate CSOs have included upgrades in key wastewater treatment facilities, storm sewer expansions and the construction of several large CSO retention tanks to mitigate this chronic source of pollution. Existing infrastructure developments have increased DEP’s standardized CSO capture rate from about 30% in 1980 to over 80% today, as shown in Figure 2.
CSO Consent Order
In the early 2000’s, DEP developed 11 CSO Waterbody/Watershed Facility Plans (a/k/a draft LTCPs) that laid out a $2.9 billion program of targeted grey infrastructure projects to reduce CSOs and to meet applicable water quality standards at that time. As part of the 2012 agreement (i.e. CSO Consent Order) between DEC and DEP, these gray infrastructure projects were integrated in the Order with specific project design and construction milestones. Additionally, in the Order DEP committed to a $1.5 billion green infrastructure program with the goal of capturing the first inch of a rainfall on 10% of the impervious CSO areas in NYC over a 20 year period. The green infrastructure program will be implemented over time to achieve the 10% goal, as shown in Figure 3.
Building off the Waterbody/Watershed Plans, DEP is currently developing Long-Term Control Plans (LTCPs) for the City’s waterbodies pursuant to the Order. Through this process, DEP is identifying appropriate CSO controls necessary to achieve water quality standards. The Order sets forward a schedule for completion of the LTCPs.
In November 2015, DEC amended the New York State receiving water quality standards requiring that all surface waters be suitable for primary contact recreation. This rulemaking was necessary to meet the “swimmable” goal of the federal Clean Water Act. Many of the City’s waterbodies were not classified for primary contact, rather the standards were less stringent allowing for uses such as secondary contact and fishing. Notwithstanding this regulatory change, the City has submitted several of its waterbody specific LTCPs with recommendations to obtain, where feasible, the swimmable goal of the Clean Water Act. The recommendations are under review by DEC at this time and the City expects regulatory approval of these LTCPs in the next month or two. The paper and presentation will provide additional details on the proposed recommendations of theses LTCPs and provide an overview of the June 2016 submittals.
DEP’s LTCP is part of a broader commitment to improve citywide water quality and we continue to pursue new ways to manage CSO impacts in light of an ever evolving regulatory landscape. As we continue to advance our long –term planning, we remain committed to addressing CSO through a mixture of grey and green solutions and remain mindful of the financial impacts to NYC ratepayers.
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